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Old Jul 24, 2012, 02:20 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
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Stalling a 2m full house glider, best recovery methods?

In flying a new to me e-glider (eGabby) that has a 4 servo 2m wing, I noticed that if I stall it hard by cutting power, it takes some time and altitude to recover. Before recoving it felt as if I had actually lost control.

Here's the scenario as I witnessed and felt it.

1- Power on, climbing well, perhaps at a 45 degree climb, hold the angle and cut all power.

2-The nose falls to more than 45 degrees down, at which point I tried to pull it up a bit.

3-The first thing it did was rotate hard to the right. I tried correcting and then it rotated hard to the left.

4- at this point I let go for a moment to give time for things to settle down, then I was able to recover nicely but I lost several hundred feet in the process.

It's my guess that this baby was not really flying yet when I tried to level and correct and it tips stalled both ways due to the ailerons disrupting what little airflow there was.

Is this normal for an e-glider? It was rather shocking and gave me the feeling that the plane was totally out of control and felt as if I was experiencing servo failure under load or something? Very unnerving.

Thanks, comments and ideas appreciated.
Dale in AZ.
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Old Jul 24, 2012, 03:00 PM
Flagstaff, AZ
dawsonh's Avatar
USA, AZ, Flagstaff
Joined Mar 2003
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Dale:

You did all the "right" things to cause a stall and then a spin.

1- you kept flying up at a 45 angle when you cut power

2- when the nose dropped (signaling that you had stalled the wing) you pulled up elevator... reinforcing the stalled condition

3- started to spin right, corrected, and spun left. Unless you neutralize the elevator any rudder/aileron inputs only allow you to control the direction of the spin/stall.

You did the correct thing (4-) to recover... neutralized the controls. This lets the wing orient back into the air flow; the stalled condition ends; and then you can gently pull some elevator to return to level flight.

Next time don't hold the 45 line when you cut power. Instead "push" some down elevator so you level off with some forward flying speed. If you time this correctly you will maximize your height and end up flying level at cruising speed... and no stall!

Remember that stall routine... since it is a fun way to lose altitude when you need to.

Dawson
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Old Jul 24, 2012, 04:04 PM
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Dale, I am also guessing that your CG might be forward too. That makes the stab have to work harder and if as it was pointed out above, you are not letting the ship get back to flying speed, you are asking the stab to have to produce a higher force than it can to bring the nose up. I am guessing that the model flies fairly fast in normal cruise and it takes a fair amount of throw to thermal?

Marc
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Old Jul 24, 2012, 04:05 PM
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Sounds like the plane did what you asked it to do...

Control surfaces need air moving across them to work...That means your plane isn't going to respond to your input UNTIL it gains enough airspeed. Hopefully before it meets the ground...
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Old Jul 24, 2012, 04:08 PM
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I wonder if inputting aileron in the direction of the spin would do anything?
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Old Jul 24, 2012, 04:17 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
326 Posts
I confess to doing the hard stall on purpose. As a full scale pilot I like to fly my glider to a stall and really feel how it responds on occasion so that I know "before" an actual stall in a critical case what the warning signs are. Thus I expected the soft controls and slow to respond.

What I didn't expect was the 2 spins. I can't get my full size glider to spin unless I hard stall and cross the controls. I did not cross them at all here, just added input and boom there it went and in both directions too!

What I believe after reading the comments is that cutting power in that big nose up attitude really caused a major stall, enough so that it had the energy to actually enter a spin which it did.

Since I am new to gliders with power, would adding power have helped in this recovery? My guts tell me this would have been an option and I was going to try that next but was able to get control after going neutral for a second or so.

Again, the violent spins really shocked me, my friend who was watching asked me what in the heck that was all about ;-)
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Old Jul 24, 2012, 04:45 PM
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Violent spins, fly a V-tail with a really aft CG and hold on, I rememeber someone telling me that any stall produced at least two turns and maybe more. That can leave you needing air.

Marc
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Old Jul 24, 2012, 10:50 PM
Trex 700, Gaui X5, 450DFC
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United States, AZ, Queen Creek
Joined Apr 2010
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To answer some of my questions I took the Gabby out for a spin this evening. It was a bit windy due to thermals aka dust devils and a prevailing westerly evening wind too but it was worth it.

1, the eGabby does in fact stall hard. Even slowing up too much on a turn and the inside tip (the one flying the slowest) stalls hard in a near vertical wing drop. Waiting just a moment for some speed is all it takes for a clean recovery.

2, adding power does in fact speed up the recovery and is something I will use after testing this out.

3, adding in a little flaps allows the glider to fly much slower w/o as much risk of stalling. Of course this makes sense since takeoff is normally with a notch or two of flaps to lower the stall speed.

Now I just have to figure out how to get these flaps to be more effective at bringing this baby down. I could push in full down elevator and it would still fly forward without much descent with 65 or so degrees of flaps. I think I need more flaps, and more elevator.
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Old Jul 24, 2012, 11:52 PM
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Your telling me that when you cut the motor off you have problem of keeping the plane level, that is a sure sign of a cg problem, is anything slopping around inside while turning in air? Trying to control a sailplane with bad cg is horrid and scary. Use latex foam (same as mouse pad material) and put it into cockpit so nothing sloshes around once you have CG correct per manual. Then to work the thermals and stay up you have to use the method of ails up and flaps down slightly to work thermals. If you get stuck in a thermal full slaps down or full flaps down and full aills up will bring it down quick.
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Old Jul 24, 2012, 11:58 PM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
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I do not believe anything can be moving in flight, it's fairly tightly packed in there. It flies pretty well normally, it just seems to stall harder than I'm used to. It's managable, just means I need to keep the speed up in turns.

I'll experiment more with flaps when thermalling to keep it from falling off that stall edge ;-) I'm also dialing back the end points on the Aileron throws, I think I had too much and was increasing the problem.

In the meanwhile I'll see if I can find anything that would tell me where the CG on a Gabby/eGabby is supposed to be. This was originally for sale from NESail and I don't see anything there anymore. Maybe someone knows this? Perhaps a forum post or is there someplace to search for such info? To get things where I have them, I carefully weighed what I took in and out as I modified it to make sure I kept it the same as when I bought it.
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Last edited by SoarWest; Jul 25, 2012 at 12:08 AM.
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Old Jul 25, 2012, 12:18 AM
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^ Is this the manual?
http://www.docstoc.com/docs/4931031/...g-instructions

It calls for 40% back but I think they made a typo and it is suppose to say 40mm back from leading edge it should balance. If you have a great planes cg machine it is a great investment.
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Old Jul 25, 2012, 12:47 AM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
326 Posts
It looks like I have some reading to do! Thanks for that great link.

Now what is a Great Planes CG Machine? Looks like something else I'll have to investigate.

My guess is that I have the controls moving TOO much and possibly a CG issue, I'll read, figure this out and report back.
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Old Jul 25, 2012, 12:51 AM
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CG machine.

Two pencils with the erasers sanded to a wedge and a block of foam or wood is all one needs.
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Old Jul 25, 2012, 01:20 AM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
326 Posts
Peter, that is precisely what I use... but I add those pointy tipped erasers ;-) As shown here.

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Old Jul 25, 2012, 01:26 AM
Trex 700, Gaui X5, 450DFC
SoarWest's Avatar
United States, AZ, Queen Creek
Joined Apr 2010
326 Posts
Upong investigating this further I found a few things I'll need to fix. That is surely typical when purchasing a used plane.

1, the elevator servos bind if I add more throw. I need to add more down since with full flaps and full down I was barely going down ;-)
2, I found what is probably part of my problem with the ailerons. They have snapped lose from the glue that was holding them in place in the wings. I'll have to figure out how to attach them a bit better... hmmmm. Right now it's primarily the tape cover holding them secure. Seems it coulld be a big problem on a hot day under load!

In looking through that manual (Thanks SOOO much for that link!) I will NOT be able to get the suggested aileron throw on the up side, they physically don't move that much, so that must be a typo. I did reprogram the setup to have less on the down than the up and that should keep turns cleaner.

I found this old thread with some CG advice.
http://www.rcgroups.com/forums/showt...ighlight=gabby

My ship is right at 80mm so I'm in the same range as they are looking. Perhaps a bit back

You guys ROCK... thanks. I want to make some time and build one, that is very fun! Of course it won't be a Gabby but something 2M and similiar
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Last edited by SoarWest; Jul 25, 2012 at 01:48 AM.
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